1. Field of the Invention
Embodiments of this invention relate to environmentally compatible materials used in fluid compositions such as drilling fluids, drilling muds, kill fluids, and cement compositions for oil, gas, water, or geothermal wells or the like that have a desired high density, while retaining other fluid properties such as pumpability, gas tight sealing, low tendency to segregate, and reduced high temperature cement strength retrogression. Embodiments of this invention also relate to densified fluid compositions suitable for cementing zones, which are subjected to extreme static or dynamic stresses. Embodiments of this invention also relate to fluid compositions for use in the drilling and completion of oil and gas wells, which form a buffer between and prevent the mixing of various fluids used in the drilling and completion of oil and gas wells so called spacer fluids.
More precisely, embodiments of this invention relate to environmentally compatible materials used in fluid compositions such as drilling fluids, drilling muds, kill fluids, and cementing compositions for oil, gas, water, injection, geothermal wells and/or other subterranean wells, where the compositions include a weighting or densifying system including at least one metal silicon alloy or a mixture of metal silicon alloys. Other embodiments of the weighting system of this invention may include metal silicon alloy or mixtures of metal silicon alloys along with other conventional densifying agents so that a density of the resulting fluid composition and an amount of the weighting system added to the fluid composition may be adjusted to achieve desired final fluid composition properties.
2. Description of the Related Art
During the drilling of deep oil and gas wells, over-pressured (or geopressured) zones are occasionally penetrated. In cases where the pressure gradient of these zones exceeds the hydrostatic pressure, fluids that use conventional densifing or weighting agents with Specific Gravity of less than 6 can be used to control the pressure, however in many cases these conventional weighing agent will not achieve the required fluid properties needed to complete the well and are often not effective where the exposed zones have a low parting pressure.
Many problems are incurred when drilling into over-pressurized zones with mud too light to hold back the gas pressure. Such resulting conditions range from gasified mud (in low permeability formations), controllable kicks which are successfully stopped by closing blow-out preventors, to uncontrollable blow-outs. To counteract the over-pressurized zones, high density fluid is pumped into the annulus (backside), drill pipe or casing (if no drill pipe is in hole). If successful, hydrostatic fluid pressure control will be established with respect to the over-pressurized zone. In the case of a blow-out, the surface or intermediate casing is often parted exposing the borehole to any proximate fresh water aquifers. Additionally, during kill operations, there is often a danger the casing will part before control is established. Furthermore, kill operations for blow-outs are not always successful and kill fluids can be blown from the well and sprayed across the countryside. Hence, any toxic chemicals included in the high density fluid could be transmitted through the aquifer, or directly through the blow-out, to the local animal and plant population.
A variety of drilling fluids and weighting agents are presently on the market. Generally, drilling fluids have an aqueous or hydrocarbon base. One principal requirement of a good drilling fluid is that it is able to suspend a sufficient amount of weighting additives so as to meet desired density requirements particularly with respect to preventing gasification and blow-outs, while remaining pumpable. With respect to aqueous base drilling fluids, a variety of water thickeners are also known. Examples are organic materials such as xanthan gums, aluminum containing compositions, such as hydrous aluminum oxide, polyacrylates, polyacrylamides and a variety of cellulose derivatives. Examples of known weighting materials include barite, hematite, calcium carbonate; zinc, potassium or sodium halides or phosphates and formates.
Under certain conditions conventional mud systems can be weighted up to thirty (30) pounds per gallon using galena as the weighting agent. Other carrier fluids such as zinc bromide and calcium bromide can also be used to carry galena. Lead powders have also been used to increase the density of zinc bromide carrier fluids. However, when wells are in communication with an aquifer the use of any metal or soluble material considered toxic is unacceptable. Additionally, the heavy carrier fluid would not be permitted to contain soluble, transmittable bromide and zinc.
With respect to blow-out control fluids, two desired qualities are good pumpability and a sufficiently high density to equilibrate downhole pressures. In blow-out situations environmental considerations receive additional attention since there is a greater likelihood of communication with an aquifer as well as the possibility of expulsion of fluids during blow-out. The density of fluid necessary for equilibration purposes is also dependent upon the well parameters.
Cement compositions, when utilized in oil field applications, must be readily pumpable and must have sufficiently high densities to equilibrate downhole pressures in the subterranean formation. When the formation is in communication with underground water, such as from an aquifer, the use of metals or water-soluble materials considered toxic is unacceptable. In addition, high density cement compositions find further application as buoy ballasts, ship ballasts, and grouting material.
In cementation of oil wells, a cement slurry is pumped down into a casing and back up the annular space between the outside of the casing and the wall of the well. The two most important purposes of the cementation process are to prevent transport of gas and liquid between subterranean formations and to tie up and support the casing pipe. In addition to sealing oil, -gas- and water producing formations, the cement also protects the casing against corrosion, prevents gas- or oil-blow-outs as the cement slurry seals the well quickly, protects the casing against shockloads and seals off formation having lost-circulation.
The setting time of the cement slurry must be adjusted to ensure that the cement slurry does not set before the slurry reaches the right location when pumped into the well. The setting time which is needed will among other things depend on the depth of cementation and on the temperature in the well.
The density of the cement slurry is important for cementing processes. For oil wells drilled through high pressure formations, cement slurries having a high density are used in order to avoid uncontrolled blow-outs. For oil wells which are drilled through low pressure formations where it is not advisable to expose the formations to high hydrostatic pressure, cement slurries having a low density have to be used, as a cement slurry having a too high density and thereby a high hydrostatic pressure may result in breakdown of the formation and loss of the cement slurry into the formation (lost circulation).
Another important property of the cement slurry is early strength. The early strength is critical for determining how quickly the drilling procedure can be restarted after the cementation process is completed. Cements which have a compressive strength after 24 hours of at least 1.5 MPa are usually satisfactory. The development of the early strength of the cement slurry is very dependent on the temperature in the well.
For cement slurries which are used for cementation of high temperature wells it is further important that the cement slurries do not lose their strength during time. It is known that at temperatures above about 110° C., ordinary Portland cement slurries over time will lose their strength as the normal binding phase, calcium hydroxide, is transformed to alpha-dicalcium silicate. This phenomenon is well known and is called cement strength retrogression.
High density cement slurries are produced by adding an inert high density filler material such as barite to an ordinary oil well cement slurry including Portland cement, water and additives for controlling the rheological properties of the cement slurry. The density range for so-called high density oil well cement slurries is from about 2.0 to 2.3 g/cm3.
As set out above, high density cement slurries for oil well cements which are either gas tight or have a low tendency of strength retrogression at high temperatures are known. The primary disadvantage of the known high density cement slurries for cementing of oil wells, is that the high density filler material required affects the compressive strength of the cement and has a tendency to settle or sag as the temperature increases. The settling of the high density filler material will result in a variable density in the column of cement slurry with a higher density at the bottom of the column and a lower density at the top of the column. This difference in density can give the operators problems in controlling the pressure in the well and may in the worst case cause an uncontrolled blow-out.
In rotary drilling of wells, a drilling fluid is usually circulated down the drill string and back up the annulus between the drill string and the wellbore face. The drilling fluid can contain many different chemicals, but will most often contain a viscosifier, such as bentonite. When a casing string or liner is to be cemented into the wellbore, any drilling fluid and remnants of the viscosifier present in the wellbore are preferably removed to aid the bonding of the cement between the casing string or liner and the wellbore. In removing this drilling fluid from the wellbore and to clean the annulus, a wash or spacer fluid can be introduced ahead of a cement slurry.
Spacer fluids are conventionally used in cementing operations related to well completion in the following manner. Drilling fluids and cement slurries are typically chemically incompatible fluids which undergo severe gellation or flocculation if allowed to come into contact. Thus, drilling fluid must be removed from the wellbore annulus immediately prior to cement slurry placement. Spacer fluids are pumped between the drilling fluid and the cement slurry to form a buffer and prevent the drilling fluid and the cement slurry from coming into contact.
Spacer fluids should also possess certain rheological tendencies, such as turbulent flow at lower shear rates, which assist in granular solids removal and which encourage the removal of the drilling fluid filter cake from the walls of the well. Indeed, a common cause of failure in primary cementing is the incomplete displacement of drilling fluids which results in the development of mud filled channels in the cement. These mud filled channels may be opened during well production permitting the vertical migration of oil and gas behind the casing.
U.S. Pat. No. 4,584,327 disclosed high density fluids including water; a gelling agent selected from the group consisting of oxides of antimony, zinc oxide, barium oxide, barium sulfate, barium carbonate, iron oxide, hematite, other irons ores and mixtures thereof wherein said gelling agent has an average particle diameter size in the range of from about 0.5 to about 10.0 micrometers; hydraulic cement wherein said hydraulic cement has an average particle size in the range of from about 30 to about 200 micrometers wherein said hydraulic cement and said gelling agent have a physical makeup with regard to fine particle size, high density and intersurface attraction properties sufficient to create a slurry with said water that has a gel strength of at least 10 pounds per 100 square feet; and a weighting material selected from the group consisting of iron powder, hematite, other iron ores, steel shot, tungsten, tin, manganese, iron shot, and mixtures thereof wherein said weighting material has an average particle diameter size of from about 2 to about 20 times the average particle size of the gelling agent; said fluid having a density of from 24 pounds per gallon to about 40 pounds per gallon.
U.S. Pat. No. 4,935,060 disclosed hydraulic cement slurries include 5-85% microsilica based on the weight of cement; 5-250% of a high density filler material based on the weight of the cement, said high density filler material selected from the group consisting of barite, hematite and ilmenite, 0-5% of a retarder (dry weight) based on the weight of the cement, 0-12% of a thinner (dry weight) based on the weight of the cement, 0-8% of a fluid loss additive (dry weight) based on the weight of the cement, 0-30% of a silica material based on the weight of cement, said silica material selected from the group consisting of silica flour and silica sand, and water in such an amount that the cement slurry has a density between 1.95 and 2.40 g/cm3.
U.S. Pat. No. 5,030,366 disclosed spacer compositions including sulfonated styrene-maleic anhydride copolymer, an ethoxylated nonylphenol surfactant, and water.
U.S. Pat. No. 5,789,352 disclosed spacer compositions including a hydrous magnesium silicate clay selected from the group consisting of sepiolite and attapulgite present in an amount in the range of from about 15% to about 85% by weight of said composition; silica present in an amount in the range of from about 15% to about 85% by weight of said composition; and an organic polymer selected from the group consisting of whelan gum, xanthan gum, galactomannan gums, succinoglycan gums, scleroglucan gums and cellulose and its derivatives present in an amount in the range of from about 0.5% to about 10% by weight of said composition.
U.S. Pat. No. 6,742,592 disclosed methods of cementing a zone of a well, comprising pumping into the well a cementing composition which comprises: (i) a hydraulic binder; (ii) a particulate material that has a specific gravity of greater than 3; and (iii) reinforcing particles which: comprise a flexible material; have a density of less than about 1.5 g/cm3; have a Poisson ratio of more than 0.3; and have an average grain size of less than about 600 μm.
Thus, there is still a need in the art for environmentally compatible high density fluid composition which is suitable for use in subterranean drilling and blow-out control, or as a cement composition which is suitable for use in oil field applications or grouting applications, or as a ballast for ships or buoys.